I'm using an L293D motor driver chip along with an HC-05 Bluetooth module. The two work as expected separately - I can send a string via a Bluetooth terminal app on my phone to the HC-05 and I see it in the serial monitor just fine, and I can use the serial monitor to change the speed/direction of the DC motor without an issue. However, if I try to use the Bluetooth console on my phone to change the speed, the motor only spins for about a second before I lose connection with the HC-05 and it stops.

I think this is happening because the Arduino is tripping some breaker by drawing too much current to power both the HC-05 chip and the DC motor. Is this the case? Should I use an external battery pack to power the DC motor and L293D chip, and then keep the HC-05 connected to the 5V out line on the Arduino?


  • Either that or the motor is causing EMI that is disrupting your communication. – Majenko Jun 7 at 19:03
  • How are you powering everything currently? – chrisl Jun 7 at 19:22
  • @chrisl Previously I was powering everything off of the 5V line on the Arduino, but I just switched to using an external battery pack of 4 AAs and that seems to work fine. – javathunderman Jun 7 at 19:59
  • Will you post a scheme of your device plase? It is Hard to ubderstand What is going on without it... As I have understood, you May have a leak of power there.. Try to power your motors using an external way: to connect them In parallel with your arduino board. Yor problem also May be caused by that your power source is not String enough, and it May be not enough it's power to keep motirs and hc05 working at the same time. Also, if you are using a board with severak uart pins on it, you May check if you haven't connected you motors to thise Uart pins I hooe my answer wil help you – user66878 Jun 9 at 20:31

Previously I was powering everything off of the 5V line on the Arduino, but I just switched to using an external battery pack of 4 AAs and that seems to work fine.

That suggests, that your power source was not strong enough. You didn't say, how you are powering the Arduino, but I guess you are doing so via USB. The USB port of a PC can only give you 500mA of current (at least without any extra configuration to get more). Also the parts on the Arduino (for example the diode between USB power and the 5V pin) can only give you a limited amount of current. Especially when the motor is starting, the needed current is rather big. That might have caused a short voltage dip, deep enough to irritate the HC-05 module.

Using an extra battery as power source for the motor eliminates that problem. Though I think you should be able to connect all parts to the same power source, as long as it is powerfull enough to power all parts (plus some overhead). In that case be sure to connect the power for the L293D and Arduino in parallel, so that the motor current does not have to flow through the Arduino (which could kill the voltage regulator or the diode).

Depending on your motor, it also might generate a huge amount of EMI (Electromagnetic Interference) either though air transmission or through the power lines, which might irritate the HC-05 enough. In that case the easiest option would be to add a second power source. Though I think the problem is with the power source as described above.

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